Toxoplasma gondii is a significant cause of disease in congenitally infected infants and patients with alterations of the immune system. The disease is perpetuated in nature by encysted forms of the parasite, either as undercooked meat infected with tissue cysts or as oocysts in food or water contaminated with cat excrement. The overall purpose of this proposal is to decipher the molecular events involved in this process, focusing on the structure and function of carbohydrate residues found in the cyst wall. The specific aims of the proposal are directed at a) elucidating structural and biosynthetic aspects of N-acetylglucosameine (GlcNAc) and N-acetylgalactosomaine (GalNAc) containing carbohydrate moieties which have been identified in cyst walls and b) relating these aspects to the biological role of these structures in differentiation of the parasite. The first aim is to determine the structure and linkage of GalNAc and GlcNAc residues in cyst glycoconjugates with the long term objective of studying their biosynthesis and ascertaining whether they serve as precursor moieties for the synthesis of the cell wall which is a key event in differentiation. The second aim is to characterize and purify chitin synthase which is developmentally regulated enzyme involved in the biosynthesis of chitin. These studies will facilitate the long term objective of delineating genetic control for differentiation at the molecular level by identifying cyst specific genes encoding developmentally regulated proteins involved in the biosynthesis of cell wall polysaccharides. The last aim is to relate the findings obtained at the structural and biochemical level to growth and differentiation of the parasite in vitro as well as in vivo in the murine model of toxoplasmosis. The ultimate goal is to design strategies to arrest differentiation, interrupt the life cycle of the parasite, and control spread of disease.